An antenna may include a transducer (e.g., transceiver) designed to transmit and/or receive radio, television, microwave, telephone and radar signals, i.e., an antenna converts electrical currents of a particular frequency into electromagnetic waves and vice versa. Physically, an antenna is an arrangement of one or more electrical conductors that is configured to generate a radiating electromagnetic field in response to an applied alternating voltage and the associated alternating electric current, or that can be placed in an electromagnetic field so that the field will induce an alternating current in the antenna and a voltage between its terminals.
Portable wireless communication electronic devices, such as mobile phones, typically include an antenna that is connected to electrically conducting tracks or contacts on a printed wiring board (PWB) by soldering or welding. Manufacturers of such electronic devices are under commercial pressure to increasingly reduce the relative physical size, weight, and cost of the devices and improve their electrical performance.
To minimize the size of an antenna for a given wavelength, a microstrip antenna (also known as a printed antenna) may be used inside a portable wireless communication electronic device. A microstrip antenna can be fabricated by etching an antenna pattern (i.e., a resonant wiring structure) on one surface of an insulating dielectric substrate having a dielectric constant (∈r) greater than 1, with a continuous conducting layer, such as a metal layer, bonded to the opposite surface of the dielectric substrate that forms a ground plane. Such an antenna can have a low profile, be mechanically rugged, and relatively inexpensive to manufacture and design because of its incomplex two-dimensional geometry.
One of the most commonly employed microstrip antennas is a rectangular patch. The rectangular patch antenna is approximately a half wavelength long section of rectangular microstrip transmission line. When air is the antenna substrate, the length of the rectangular microstrip antenna is approximately half of a free-space wavelength. As the antenna is loaded with a dielectric as its substrate, the length of the antenna decreases as the relative dielectric constant of the substrate increases. That is, the wavelength of the radiation in the dielectric is shortened by a factor of 1/√∈r. An antenna including such a dielectric substrate may therefore be made shorter by a factor of 1/√∈r.
Many portable wireless communication electronic devices include antennas to provide cellular system communication functionality, for example, GSM, or WCDMA communication functionality, and/or antennas to provide non-cellular system communication functionality, for example, Bluetooth, W-LAN, or FM-Radio communication functionality. The number of supported systems directly increases the number of required antennas, which results in a substantial increase in the component part count and, consequently, the size and cost of the electronic devices themselves.